Four-wire signaling circuits



July 9 1940 N. BoTsFoRD FUR-WIRE SIGNALING' CIRCUITS Filed Nov. 5, 19382 Sheets-Sheet 2 FOUR -W/RE C/RCl/l T Faun-WIRE c/Rcu/r /IV VE /V TOR NQQQQQIO n l2 u lo Il 8 g A TTOR/VE V Patented July 9, 1940 UNIT-ED'STATES 2,207,531 .e x l l FOUR-WIREr SIGNALING jerectil''rs f NelsonBotsford, Rutherford, N. J., assignor to Bell Telephone Laboratories,Incorporated, New York, N. Y., a corporation of N ew York. f

vApplication November 5, 1938, SeriallvNo. 239,005

1 Claim.

i' This invention relates to signaling circuits embodying hybrid coilsand more Aparticularly to hybrid coil arrangements for associating two`wire circuits with four-wire circuits.

He'retofore hybrid coil arrangements have been used in signalingcircuits for connecting a two-wirel circuit with a `four-wire circuit.Certain'ofsuch arrangements are disclosed in the patent to H. NyquistNo. 1,504,135, granted August v5, 1924. The present invention is animprovement over the Nyquisty circuit in that provisionis made forminimizing or obviating the effects of .longitudinal currents induced inthe two-wire circuit. The eifects of these currents are blocked vfromthe four-wire circuit thereby precluding interference therein with thetransmission of v signaling currents.

It is an object of the present invention to provide a Ahybrid coilarrangement for coupling a two-wire circuit to a four-wire circuit in amanner su'ch that the effects of longitudinal cur. rents in the two-wirecircuit are canceled and' therefore do not appear in the four-wirecircuits. .In'a preferred embodiment the invention comi '.5 prisesrapair of multiwinding inductance coils,

two windings of the one connected in series with twol windings of theother and both pairs applied to a two-wire circuit. A mid-point of thesewindings is connected to ground. Accordingly, o longitudinal currentsinduced in the two-wire circuitv flow to ground in opposite directionsin each of the two windings on the saine core. This causes the flux dueto the longitudinal current in one winding to oppose the flux due to thelongitudinal current in the other winding on the same core.Consequently, the effects of the longitudinal currents are calceled andtherefore do not reach` the four-wire circuit.

v`The invention will be more readily understood from the followingdescription taken together with the accompanying drawings in which: y

Fig. l is a circuit diagram showing a preferred embodiment of theinvention;

Fig 2 is a circuit diagram illustrating a modi-v fication oi Fig. 1;

Fig. 3 is a circuit diagram showing an alternate form of the invention;and

Fig. 4 is a circuit diagram showing the invention used in a signalingsystem for deriving phantom'circuits.

In the drawings the same reference numerals are' employed to designateidentical elements appearing in the several gures.

Fig. 1 shows a two-wire two-way transmission circuit L associated withtransmission paths L1 and L2 through a hybrid coil I3.l The paths L 1and L2 may: constitute the four wires of a four` wire circuit, 'or thoseleading to a four-wire repeater circuit, Butone end of the four-,wirecircuit is shown. Afor Lthe reason that the other end 5 is identicaltherewithfand is well understood in theart.;"fA n The hybridrcoil yI 3comprises individual coils I4 and I4a,.eachcoil including tsix windings,I6, n, la and is, which are preferabiy wound as a 1 quad although woundin layers would serve, equally as well'fas long as they are wellbalancedand closely coupled and a pair of seriallyconnected. windings2:0 and2I.` The windings I8 and I9 on coil I4 are connected in seriesand the windings Iiiaand .I 9c on coil I 4a are also connected inseries. 'In addition, the windings I 8 and.

I 9 are connected in series with the windings I 8a and I9a, aiicbtheterminals 9 and I2 of the respectivewindings 19a and I9 are applied toa- 20 well-known balancing network N. It is understood that .thecoilsI4`and Illa are provided withy cores ,of` suitable magnetic material onwhichthe various windings are wound. p

The winding I6 oflcoil I4 is connected in series 25 with theA windingIlia on coil I 4a, the latter winding being connectedin `series with thewinding I "la: on: the4 same coil. v'I'he winding I'Ict is alsoconnected in serieswith the winding I 1 on the coil I4. yThe terminals 5and 8 of the respective 3 windings I6 andv I'I are applied to thecircuit L. 'I hus the arrangements of the windings I6 and I'I on coilI4'r and of the windingsy I 6a and Ila on coil. Illa are such that thewindings onthe same core are connected in a series-aiding relation- 35ship. The ilow of signaling current in the wind-A ings of each coil .isin ythe same direction and is indicated by the solid arrows associatedthere! with.

The'mid-poiutofV thewindings I6a and I'Ia is` 4U connected by. .alead122 to ground 23. `'Ihis also serves to "connectto groundthemid-point of the serially-connected windings I6, I6a, I'Ia and IIl.

`The serially-connected windings 20 and 2I on coil I4 serve to couplewindings I6, Il, I8 and I9 to path L1 4while the serially-connectedwindings 2Ua'and2la on `coil I4a serve to couple windings IGa, Ila, I8aand I9a to path L2. It is understood thatfthe impedance of thecircuitvL, 50

balancing network N, and paths L1 and Lz may be so related by the coilsI4 and I4a that signaling energy transfer may be accomplished in desiredproportions.v As such transfer is well under' stood in the art,- afurther discussion-thereof@ is deemed unnecessary here but reference ismade to the patent to H. Nyquist, supra.

In Fig. 1, the numerals I through I2 indicating the winding terminalsserve to designate the polarity thereof, that is, current ilowing in anywinding from an even to an odd numbered terminal produces ux in the coreassociated therewith in one direction while current flowing in anywinding from an odd to an even numbered terminal produces iiux in thecore associated therewith in an opposite direction. This is also truewith regard to Figs. 2, 3 and 4 in which the respective i-f windings ofthe hydbrid coils are similarly desig-K. nated as in Fig. 1 and whichwill Vbe hereinafter described.

The arrangement shown 1n Fig. 1 is particularly adaptable for use intoll`circuits in iwhichv1 it is desired that current from a battery281e-,k

cated at a toll oiiice be transmitted over the circuit L to a subscriberconnected to the'terminal thereof, not shown. In the event oflongitudinal or noise currents being induced in the circuit L andtransmitted toward the toll oiiice, these currents would ilow to ground23 through the windings IB, Ia, IIa and I1 in the directions indicatedby the dotted arrows. It will be observed that the noise currents flowinopposite directions through the windings I6 and II of the coil I4 andalso in opposite directions 4through the windings IBa and. I'Ia ofthecoil I4a. Hence, the flux produced inthe cores of the coils I4 and I4aand due to the rnoise currents owing in the respective windings will bein opposition. Consequently, the

effects of the noise currents willbe canceled inl the coils I4 and I4a,and will not enter either path L: or path Lz.

Thef arrangement of Fig. 1 provides for a high loss from path L1 to pathL?. for the reason that loss therebetween depends solely on the equalityof the windings I6, I1 and I8, I9 on coil I4 and of the windings Ia, Ilaand IBa, I9a on coil I4a, assuming that the impedance of the network Nequals that of .the circuit L. These windings on the individual` coilsI4 and I4a are inherently excellent since they are very closelyassociated, being wound at the same time as a quad. While winding as aquad is preferable, it is not necessarily limited thereto as pointed outhereinbefore.

Longitudinal currents on the side of the balancing network N arenormally negligible and usually there is no need of grounding themidpoint of windings I8, I9, I8a and |911. Consequently, windings I8 andI9 on coil I4 and windings l8a and I9a on coil I4a may be wound on therespective coils as a single winding. This does not affect the balanceoi the circuit L although itmay lower the loss from the path L1 to thepath L2 by placing less winding capacity across the network N than isplaced across the circuit L. The high loss from the path L1 to the pathL2 may then be brought back to a desirable level by placing a condenser26 of proper capacity across the network N in Fig. 1. Thus the condenser28 servesto render the effective winding capacity across the network Nequal to the effective winding capacity across the circuit L.

Fig. 2 is identical with Fig. 1 except the winding I9 on coil I4 isconnected in series wth the serially-connected windings I8a and I9a oncoil I4a while the latter are also connected in series with the windingI8 on coil I4. The terminals 9 and I?. of the respective windings I8 andI9 are applied to the network N. Thus the connections of the windingsapplied to the network N are equivalent from a capacity standpoint tothe connection of the windings I6, I1, Ilia and IIa applied to thecircuit L. This arrangement obviates the condenser 26 of Fig. 1.

The arrangement of Fig. 2 is particularly adaptable for use in thederivation of phantom circuits as illustrated in Fig. 4. Referring tothe latter, signaling currents flow in the physical circuits and 3| andthe respective hybrid coil sets vA and C in the directions indicated bythe solid arrows. In this connection it will be observed that the flowof signaling current in the windings oieach coil I4 and I4a comprisingthe respective .hybrid coil setsA and C is in the same direction.Transfer of signaling energy between the two- 1 wire circuits 30 and 3Iand the four-wire circuits "lassocia'ted therewithy is effected in themanner "mentioned above relative to Fig. 1.

Phantom currents` flow in the physical circuits I 3l] and 3|, the hybridcoil sets A, B, and C, and the'connetions therebetween in the directionsindicated by thedot-dash arrows. These currents flow ,in oppositedirections in the windings of the ,coilsz I4 and [4a comprising thehybrid coil sets A and C. `The Aflux due` to these currents will be inopposition in the cores associated with the respective coils I4fand,I4al and the effects of the phantom currents will therefore be canceledin the respective hybrid coil Asets A and C. Consequently, lthe effectsof the phantom currents will not reachfthe, four-wire circuit associatedwith thehybr-id coilsets A -and C. However, in the windingsof rthe coilsI4 and I4a comprising the hybridu coilset B, phantom currents iiow inthe same direction.- TheV flux due to this current in the hybrid'coil.set B, will bein an aiding relationship` and the effects of `thephantom currents will be thereforetransferred to thefourwire,circuituassociated with the hybrid coil set B. The transfer of,this energy between the twowire and .the four-wire circuits is eiectedin the proportionmentioned above in connection with Figi. .l Noise or4longitudinal currents induced in the two-wire circuits 30 and 3| inFig. 4 ow therein and in the windings of the vhybrid coil set A, B and Cto groundl 32 connected to the mid-point of the windings of the coils I4and Illa. comprising the `hybrid coil set B in the directions indicatedbythe dotted arrows in a manner siminar to that for the ow of,noisecurrents in Fig. l as explained above. .Thus the noise currentsilow in opposite directions in the windings of each of the coils I4 andI4a comprising the hybrid coil sets A, Band C. As the flux ldue to noisecurrents is also in opposition in the same cores associated with therespective coils I4.and Ida., the effects of noise currents will becanceled and will therefore not reach any of the four-wire circuits.

It is to be understood that the organization of Fig. 1 may also be usedfor the derivation of phantom circuits in the manner aforedescribed withregard to Fig.4 4.

Fig. 3 is generally similar to Fig. 1. In Fig. 3 winding I6 on coil I4is connected in series with winding Ila on coil I4a. The latter Windingis connected in series with Winding I1 on coil I4 and winding I1is-connected in series with winding Ia on coil I4a. The terminals 5 and8 of the respective kwindings `I6 and I6a are applied to the circuit L.Thus, the windings I6 and I1, and also Ilia and I la ,are arranged in aseries-aiding relationship on the respective cores. The midpoint of thewindings on the coils I4 and I4a is connected by a lead 24 to ground 25.The serially-connected windings I8 and I9 on coil I4 are connected inseries with the serially-connected windings i811 and lSa on coil Ma. Theterminals i2 and I2 of the respective windings i9 and Ia are applied tothe network N.

In Fig. 3 signaling currents flow in the two- Wire circuit L and thewindings of the coils i 4 and idc in the same direction as indicated bythe solid arrows. The transfer of signaling energy between the two-wireand the four-wire circuits is accomplished as mentioned in connectionwith Fig. l. Noise or longitudinal currents induced in the two-wirecircuit L and owing therein and in the windings of the coils I4 and Mato ground 25 are indicated in Fig. 3 by dotted arrows. It is seen thatthese noise currents ilow in oppositedirections in the windings IS andil and also in the windings ita and lla. The ux due to these currents isin opposition in the same cores and the eiects of the noise currentswill be canceled. Consequently, the effects of the noise currents willnot reach the four-wire circuit. The hybrid coil according to Fig. 3 mayalso be used in the derivation of phantom circuits in a .manner sirnilarto that illustrated in Fig. 4. This arrangement also includes thecondenser 26 whose function was mentioned above relative to Fig. 1. Theuse of this condenser may be avoided by connecting the windings appliedto the network N in such manner that the latter are equivalent from acapacity standpoint to the connection of the windings applied to thecircuit L, as mentioned above with regard to Fig. 2.

It is to be understood that the invention is not limited to the precisedetails of the circuits illustrated and described for it is apparentthat numerous modifications thereof could be made without departing fromthe spirit of the invention, the scope of which is to be determined bythe appended claim.

What is claimed is:

A hybrid apparatus for associating a two-wire circuit, a four-wirecircuit and a balancing network, said apparatus comprising a pair ofmultiwinding coils, a irst pair of windings on a first coil connected inseries, a first pair of windings on a second coil connected in series,the two first irs of serially-connected windings connected in andarranged so that one winding of .each thereof is applied to thebalancing network, a second pair oz windings on said rst coil con`neoted in series, a second pair of windings on said second coilconnected in series with the seriallyconnected second pair of windingson said first coil, each oi' the second pairs of windings disposed in aseries-aiding relationship, the serially-connected second pairs ofwindings arranged so that the second pair of windings on said secondcoil is connected to thetwo-wire circuit, the iirst and second pairs ofwindings on each of said coils applied thereto as a quad, groundingmeans, a lead connecting the grounding means to a midpoint of theserially-connected second pairs of windings so that longitudinalcurrents induced in the two-wire circuit iiow in opposite directions ineach winding of the second pairs of windings thereby canceling theeiects thereof in each of said coils, a third pair of serially-connectedwindings on each of said coils for coupling of the first and secondpairs of windings thereon to the fourwire circuit, and a capacity inbridge of the network for rendering the effective capacity of thewindings applied thereto substantially equal to the eiective capacity ofthe windings applied to the two-wire circuit.

NELSON BOTSFORD.

